You ask about a list of 'Progressive-approved boundaries'. It is a novel way to approach it and the answer is no, there is no such list, in part because everyone is different, and so we would never be able to agree one!
We expect you to be aware that there are a variety of approaches within today's Jewish world (and it was always so!). There are some tell-tale signs to be aware of - and wary of!
God - written G-d, is the first. Along with 'Hashem' (the name), these are considered by some as ways to 'protect God' and God's name from misuse. Indeed I recently went to a concert where they sang 'Hallelu-Kah' instead of Halleluyah, since Yah is a name for God (and even though I consider singing to be one of the best and most accessible ways to heightened spirituality and prayer)! If any of these are used, it is highly likely to be a very orthodox site or publication. Note that newspapers acceptable to most orthodox Jews such as the Jewish Chronicle in London and the Australian Jewish News are happy to print God and never use G-d! Rabbi Dr Jonathan Sacks has produced very many excellent books - always using 'o'! I believe the increasing use of G-d is a sign of a creeping waning in confidence in the face of ultra-orthodoxy!
If a site says 'Jews do this, Jews observe the Sabbath by refraining from driving or using electricity, Jews do that' as if all do, that is also likely to be an orthodox site, not recognising, reflecting or accepting the diversity across the Jewish people.
Progressive Jews would, I think, agree on a fairly scientific understanding of religion as part of a growing and developing civilisation. There is one power of the universe, and we assume that God a) is beyond our understanding, b) has no gender or human attributes, c) is good and does good or would do good. We attribute to God absolute justice, love, compassion, patience, forgiveness - what we would expect of a perfect human being - and then we try to act like that, 'emulating God'. We REJECT the idea that the whole Torah is God's word, dictated to Moses at Mount Sinai, and therefore inalienably true. We believe it is a human-written document, seeking to answer the question 'What does God require of us?'
So the distinction between Progressive and rigid orthodoxy (and the division in the Jewish world today) goes back to Mount Sinai. We believe some momentous event probably happened there. But we are not bound by every detail attributed to that moment and to God. Furthermore, we believe that we follow the Rabbinic tradition of interpretation and application for our own times, needs and understanding, which they innovated by saying that God gave not only the Written but also the Oral Torah - in other words you can't understand and apply the written Torah without the oral interpretation (which should never be written down). Unfortunately, it was written down, first as the Mishna, and then, after several hundred years of study and discussion and argument and compromise, and with majority and minority opinions, as the two Talmuds. By now, in written form, it began to solidify and then stagnate. Eventually Progressive Judaism developed out of the modern enlightenment understandings of the world, highlighting the ethical values, and empowered Jews to make EDUCATED choices from the ritual traditions, selecting those that helped BRING GOD INTO THEIR LIVES. When we say that we consider Progressive Judaism to be in the true Rabbinic tradition, therefore, we feel we are on very strong ground!
However, it may be that, once you have done this reading and exploration, you will decide that this is not the path that resonates for you. Whatever path you decide on for the time being, we recognise that it is your choice and your right, and we will be here if and when you need our support and assistance.